1. Field of the Invention
The present invention relates to a new device for shaking a pump located downhole in a well for the purpose of freeing a stuck or obstructed ball valve located in a valve cage of the downhole pump. More specifically, the present invention is a device having a top end provided with a cap which screws into a sucker rod coupling and a bottom end provided with a piston which screws into either a sucker rod coupling or the pump, the device thus forming a link in the rod string at or near the downhole pump. The cap attaches to a cylinder forming a ceiling for a compartment located within the cylinder. The compartment has an opening which forms a floor for the compartment and through which the piston extends so that a head of the piston is movably confined within the compartment. The head travels within the compartment in response to the up and down movement of the rod string, striking the ceiling or floor of the cylinder with each stroke, thus shaking the downhole pump.
2. The Prior Art
A preliminary search was conducted on the invention disclosed herein, and the following listed patents were uncovered in the search:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 969,489 J. B. Oeink Sept. 6, 1910 Re 20,312 P. G. Gates March 30, 1937 2,245,128 C. J. Gardner June 10, 1941 2,687,179 N. B. Dismukes Aug. 24, 1954 3,036,647 O. L. McCracken May 29, 1962 3,209,834 R. L. Essary Oct. 5, 1965 3,642,069 Adkins Feb. 15, 1972 4,846,273 Anderson, et al. July 11, 1989 ______________________________________
Pumps used downhole in wells normally are provided with ball valves which allow gases and fluids to move upward from the pump but prevent them from moving downward again. Frequently during operation, these ball valves become stuck or a piece of debris becomes lodged therein, preventing the valve from operating properly. When a ball valve becomes stuck or obstructed, a way of freeing the valve is needed.
Several methods have been employed to clear valves on downhole pumps. One method includes lowering the pump to the bottom of the well so the pump scopes together in the hope that this maneuver will free the valve. This method can damage the pump or loosen the pump threads when the pump is scoped together.
Another method employed to clear the valve on downhole pumps includes pulling the pump out of the well and physically freeing the valve. This method is time consuming and costly and, therefore, is usually employed as a method of last resort.
Devices for mechanically moving the ball in order to clear the valve downhole have been incorporated into the design of pumps. For example, U.S. Pat. No. 969,489 reveals a pump part including a pin which strikes the ball on the downward stroke, thus knocking the ball free.
These pump devices have several problems. First, they must be made to fit each pump size and design. Because of the large number of pump sizes and designs, a large inventory is required to be kept in stock in order to be able to quickly fit a pump which might require a replacement for this part.
Second, these devices are part of the pump and are essential to the pump's function. They cannot be removed from the pump or placed onto the rod string anywhere except in the pump. Removable of the devices requires disassembly of the pump, a procedure which is costly and time consuming and, therefore, is undesirable.
Finally, U.S. Pat. No. 969,489 is designed to fit a tubing pump. The device does not fit a modern pull-rod insert pump and possibly will not work on any of the modern day insert pump and plunger lift systems.
The remaining patents listed above are not considered sufficiently pertinent as to require any comment.
The present invention overcomes the problems of prior art devices for clearing ball valves downhole by employing universal threading for use on standard rod sizes. This allows the invention to fit a wide range of wells with only a few sizes which are threaded for standard rod threads, thus reducing the cost of production and inventory of the devices.
The present invention screws onto the rod string as a joint in the rod string. It can be installed anywhere in the rod string and can be removed simply by unscrewing it at both of its ends from the rod string and reconnecting the rod string.
Finally, the present invention is designed to fit and function on modern insert pump and plunger lift systems.